1. Field of the Invention
The present invention relates to an ink jet printing apparatus that uses a print head with a plurality of ink ejection nozzles to form an image and to a recovery device and a recovery method for maintaining an ejection performance of the print head in good condition.
2. Description of the Related Art
A printing apparatus of an ink jet printing system that forms an image by ejecting ink droplets onto a print medium uses a print head having formed therein a plurality of minute ejection ports and ink paths communicating with them (all these are generally referred to as nozzles). In this ink jet printing apparatus, ink may become more viscous or solidify adhering to nozzles because of bubbles and dust entering from the ejection ports into the ink in the paths or because of evaporation of solvent contained in the ink. If this happens, the ejection performance of the print head degrades significantly. That is, problems arise with the print head, such as landing deviations of ejected ink droplets and a failure to eject ink droplets. To avoid such ejection performance degradations of the print head, a conventional practice involves refreshing ink in the nozzles to discharge viscous or solidified ink from the nozzles. This process is called an ejection performance recovery operation.
One form of the ejection performance recovery operation uses a cap capable of covering a face of the print head formed with ejection ports and a pump connected to the cap. In this configuration, the cap covers the ejection port surface of the print head and the pump generates a negative pressure in the cap to forcibly suck out ink from the nozzles of the print head. Thus, this ejection performance recovery operation is also called a suction-based recovery operation.
Another form of the ejection performance recovery operation involves driving ink ejection energy generation devices in the nozzles with the cap opposed to the ejection port surface of the print head. This causes viscous ink or ink containing bubbles and dust to be ejected into the cap, refreshing the ink in the nozzles.
The ink received during the ejection performance recovery operation into an ejection performance recovery device, including the cap, pump and waste ink tube communicating with these, is led toward a waste ink tank. This is accomplished by operating the pump with the cap open to the atmosphere, a so-called open suction operation.
There are other factors responsible for the deteriorated ink ejection performance, such as ink and paper dust adhering to the surroundings of the ejection ports. To remove these ejection failure factors, another ejection performance recovery operation is also performed which wipes the ejection port surface of the print head with a blade (referred to as a wiping-based recovery operation).
In this wiping-based recovery operation, viscous ink and dust may solidify and accumulate on the blade as a result of its wiping action. When the ink and dust solidify on the blade, the recovering capability of the blade deteriorates significantly. Thus a method has been proposed which ejects ink from the print head onto the blade to clear the blade of the viscous ink and dust (Japanese Patent Application Laid-open No. 7-164643 (1995)). Further, Japanese Patent Application Laid-open No. 2-095862 (1990) discloses a method of removing the ink sticking to the blade by performing a preliminary ejection while the blade is wiping. The preliminary ejection means an ink ejection, not contributing to the formation of an image, which is performed at the beginning of a printing operation to keep the ejection performance of the nozzles of the print head in good condition.
The printing apparatus at times ejects a large number of ink droplets and a large volume of ink as during the printing on a large area, continuous printing or high-duty printing. During such printing operations, ink easily remains on the ejection port surface of the print head and on the blade either in a solidified state or highly viscous state. The conventional techniques described above may not be able to remove sticking ink thoroughly from the ejection port surface of the print head.
More specifically, in the ink jet printing apparatus of Japanese Patent Application Laid-open Nos. 7-164643 (1995) and 2-095862 (1990), the recovery operation using the blade is always performed only a predetermined number of times. It may not be possible, therefore, to thoroughly remove the ink remaining on the ejection port surface or on the blade when the ink is solidified or viscous. Particularly when ink solids adhere to the blade, the blade with a degraded ink removing performance cannot remove ink from the ejection port surface of the print head satisfactorily.
As described above, the conventional techniques used in the above patent documents may not be able to keep the ink ejection performance of the print head in good condition at all times and thus cannot prevent an ejection failure of the print head or degradation of ink landing accuracy well.